1. A four channel differential scanning calorimeter of the heat- flow type has been constructed (with C.P. Mudd), calibrated and placed into operation. The computer software required for data acquisition and analysis has been written (with T.R. Clem) and tested. This instrument will markedly increase experimental throughput. 2. The thermodynamic basis of the destabilization of some DNA dodecamers caused by the introduction of purine-purine base mismatches has been found to be wholly of entropic origin. This investigation (with F.B. Howard and H.T. Miles) has demonstrated that it is mandatory to carry out calorimetric experiments to validate the significance of any apparent thermodynamic parameters that may be derived from the temperature dependence of spectroscopic measurements. The failure to obtain meaningful thermodynamic parameters for these molecules from these optical methods, indicates that great caution must be exercised in their application.